Method of determining conjugate centers of percussion of railway cars



E. P. MOSES METHOD OF DETERMINING CONJUGATE CENTERS OF Oct. 17, 1944. 2,360,706

PERCUSSION OF RAILWAY CARS Filed Jan 23 1942 INVENTlSIL H14 1 P d- 5.

. A TTORNEYS.

Patented Oct. 17, 1944 METHOD OF DETERMINING CONJUGATE CENTERS OF PERCUSSION OF RAILWAY CARS Edwin P. Moses, White Plains, N. Y., assignor to Railroad Rolling Stock Patents Corporation, Highland Park, Mich-.,'a corporation of Delaware Application January 23, 1942, Serial No. 427,875

4 Claims. (01. '7365) My invention relates to railway equipment and has particular relation to means adapted to be employed for improving the riding qualities of railway vehicles.

The object of my invention is to provide a mechanism for, and a method of, determining the axis of rotation of a railway car with respect to any given center of percussion, which shall be simple to operate, accurate in results, inexpensive to manufacture and durable in operation.

For a better understanding of my invention reference may now be had to the accompanying drawing, of which:

Fig. l is a side elevational view of a device embodying my invention in its operative position with respect to a railroad car.

Fig. 2 is a transverse sectional View of a portion of the structure illustrated in Fig. l, the view being taken along line 2-2 thereof.

Fig. 3 is a side elevational view of the structure illustrated in Fig. 2.

In the drawing I have illustrated a typical railroad car body I provided with the usual longitudinal body sills II and supported upon a pair of flexible or resilient supports I2 and l2 which are alike in construction. Mounted directly above one of the supports, in the drawing the support 12, is a device l3 adapted to oscillate the car body I!) upon the support l2. The oscillating mechanism [3 consists of an electric motor I4 provided with a shaft l5 on which is mounted a wheel I6 having an eccentric weight I1 mounted thereon. The motor is controlled by means of a switch and rheostat N3 of any suitable construction which will permit of producing various speeds of the motor l3.

Each of the supports 12 and I2 comprises a transversely extending bar composed of a plurality of channel-shaped metal members 2| upon each end of which are mounted two short longitudinally extending metal channel members 22 which, in turn, support a member 23 constituting a mounting for an inverted V-shape member 24 the upper edge of which is comparatively sharp so as to produce a substantially knife-edge support for the car body It! engaging the sills H.

The bar 20 is mounted at each end upon four coil springs 21 which are symmetrically arranged and which are held in position by means of an upper metal retaining plate 28 and a lower supporting and retaining metal plate 29. The plate 29 is supported upon short longitudinally extending metallic channel section metal supports 30 which in turn rest upon a plurality of transversely arranged metallic channel-shape members 3| constituting a main supporting beam. The beam is slightly greater in length than the width of the car and. rests upon any suitable supporting surface. Mounted upon the upper retaining plate 28 of the support 30 is an arm 35 upon which is mounted a dial indicator 36 having a stem 3'! protruding from the lower side thereof, any vertical movement of which is measured by the indicating gauge 36. Secured to the lower retaining member 29 of the support 30 is an L-shape arm 38 which projects beneath the indicating gauge 36 and is adapted to engage the stem 31.

It is an established fact that, in any freely movable body pivoted at a point on one side of the center of gravity, there is another point on the opposite side of the center of gravity at which application of a force in a direction adapted to produce rotation of that body will produce a pure rotation of that body about the point of pivotal support without subjecting that support to any force reaction parallel to the applied force. If the point about which the body tends to rotate is called the center of rotation the point of impact becomes the center of percussion with respect to that center of rotation, and these two points are conjugate, in that the centers of rotation and impact are mutually interchangeable.

Applied to a railway vehicle this means that,,

if the centers of suspension of the trucks are located in the vertical transverse planes of the conjugate centers of rotation and percussion, any vertical movement imparted to the car body by one truck, due to vertical irregularities in the track, will produce pivoting of the body about the center of suspension of the other truck. As this center of rotation is directly over the center of suspension of the first truck, such pivoting movement, or oscillation, will cause no compression of the springs of the first truck, which would necessarily occur if the first truck were located at any other point. In the latter case alternate compression and expansion of the springs of both trucks would necessarily take place because the centers of rotation and percussion are always conjugate, causing pitching of the car body and resulting in an unpleasant ride for the passenger. As the equipment, furnishings, etc. of a car body are not uniformly distributed with respect to the length of the car body it is desirable to be able to determine the location of the conjugate centers of rotation and percussion by fixing the location of one of those centers and determining the other by some simple accurate means.- In using this device it is necessary only to mount the oscillating member I6 within or on the car body in substantially vertical alignment with the assumed location of the efiective center of support of one of the trucks. The supporting member [2 is then mounted beneath the car body in substantially vertical alignment with the location of the center of support of the second truck which becomes the plane of the center of rotation for some center of percussion assumed to be in the vertical transverse plane of the first support.

With the support [2 located under the assumed center of percussion, the eccentric I! is rotated in synchronism with the natural frequency of the spring support, in my equipment about 170, revolutions per minute, which causes the end of the car body actuated by the eccentric H to oscillate about some point within the body at the opposite side of the center of gravity of the body as a center of rotation. If the support It is located in vertical alignment with the natural axis of rotation there will be no vertical movement of the car body at that point and the gauge 3% will indicate no movement. However, if the support 52 and the oscillator l3 are located either forwardly or rearwardly of the center of percussion the car body will move vertically up and down on the springs 21 of the support I2 and the gauge 36 will indicate such movement. The support l2 and oscillator I3, maintained in vertical alignment, are then moved forwardly or rearwardly as may be desired and the motor Hi, again operated. If the movement indicated on the instrument 35 is greater than that previously recorded the support I2 has been moved in the wrong direction, in other words, farther from the center of percussion. On the other hand, if the gauge 36 indicates a smaller amount of movement the direction of movement of the support l2 with respect to the support i2 is correct.

By means of a series of tests of this character, the number of which will be relatively small after some experience has been obtained with the equipment, a point of location of the support l2 and oscillator i3 on the length of the car can be determined at which no vertical movement of the car body occurs at support i2 regardless of the vertical movement of the opposite end of the car caused by the rotating eccentric. This point coincides with the location of the center of percussion, for the given amount and arrangement of equipment within the car body for -a center of rotation located in vertical alignment with the support IZ This point then is most suitable for the center of support of a truck provided that the truck at the opposite end of the car is located in vertical alignment with the opposite support I2 My invention has been described with the support [2 fixed in position and the support I? and oscillator I3 is movable owing to the fact that centers of percussion are always determined with respect to a given or determined axis of rotation. As a matter of practice it is easier'to consider the center of rotation and center of percussion as two conjugate centers of rotation and percussion, which they necessarily are and to place the oscillator I3 over the support [2 disposed at one assumed center of percussion, and move the support l2 toward and away from the support l2 to determine the second or conjugate center of rotation.

In instances of the character described the car body pivots about an axis, rather than a point, but the axis passes through the center of rotation producing, in reality, an axis of rotation.

Although I have illustrated but one form of my invention, and have described in detail but a single application thereof, it will be, apparent to those skilled in the art that it is not so limited but that various modifications and changes may be effected therein without departing from the spirit of my invention or from the scope of the appended claims.

I claim;

1. The method of locating the conjugate centers of percussion and thereby the proper relative positions of the supporting trucks of a railway car body with respect to the length thereof which comprises mounting the car body on one fixed and one longitudinally movable resilient support, moving said movable support to various positions at different distances from said fixed support, oscillating said car body vertically by aforce applied thereto in substantial vertical alignment with one of said supports in synchronism with the natural frequency rate of the latter support, and determining the position of the movable support at which vertical movement of the body is at a, minimum with respect to the support in spaced relation with the point at which the force was applied.

2. The method of locating the conjugate centers of percussion and thereby the proper relative positions of the supporting trucks of a railway car body with respect to the length thereof which comprises mounting the car body on one fixed and one longitudinally movable resilient support, moving said movable support to various positions at different distances from said fixed support, securing to said car body in substantial vertical alignment with said fixed support a means capable of alternately exerting on said car body intermittent vertically upwardly and vertically downwardly directed forces when energized, synchronizing the rate of application of said alternate upward and downward forces with the natural rate of frequency of the fixed resilient support with said movable support in various positions, and determining the position of said movable support at which the'vertical'movement of the car body with respect to the movable support is at a minimum.

3. The method of locating the conjugate centers of percussion and thereby the proper relative position of the supporting trucks or a railway car 'bocly'with respect to the length thereof which comprises mounting the car body on one fixed and one longitudinally movable resilient support, moving said'movablesupport to various positions at different distances from said fixed support, mounting on said car body in substantial vertical alignment with said fixed support a rotatable eccentric, rotating said eccentric and synchronizing the speed thereof with the natural frequency rate of the fixed resilient support with said movable support in various positions, and determining the position of said movable support at which the vertical movement of the body with respect thereto is at a minimum.

4. The method of locating the conjugate centers of percussion :and thereby the proper relative positions of "the supporting trucks of a railway car body with respect to the length thereof which comprises mounting the car body on 'one fixed and one longitudinally movable resilient support, securing to's'aid car body in fixed support, and determining the position of said movable support at which the vertical movement of said body with respect to said fixed support is at a minimum with said force producing means energized and synchronized with the natural frequency rate of the resilient movable support. I

EDWIN P. MOSES. 

